4 PilOCEBDINGS OP THE GEOLOGICAL SOCIETY. [NoV. 9, 



Another elaborate memoir treating of the detrital beds within the 

 Wealden escarpment, and their bearing upon the mode in which the 

 denudation was effected, is that of Messrs. Foster and Topley*. 

 The view of these gentlemen was that after a plane of marine denu- 

 dation had been effected over the original area, the whole of the 

 denudation by which, not merely the valleys proper of the Wealden 

 rivers, but also the great excavation of the "Weald itself (or major 

 valley), with its well-known contour, have been accomplished was 

 effected by these rivers, especially the Medway, flowing in their 

 present direction — a view indorsed, apparently, by Prof. Eamsay f. 



Many other notices, special and incidental, upon this question 

 have appeared, and among them notices from Mr. Martin, Mr. 

 Godwin- Austen, Mr. Prestwich, and Mr. Mackie ; the first-named 

 of whom has for a long period been a staunch upholder of the 

 marine theory; while Sir Charles Lyell, it is well known, has always 

 adhered^ in his ' Elements ' and in his ' Manual of Geology,' to the 

 same hypothesis of marine agency. 



In 1866 1 a study of the distribution of the gravel of the Thames, 

 of that of East Essex and its continuation in the lower valley of the 

 Medway, and of that of the heights above Canterbury led me 

 to the conclusion that each of these gravel-sheets had partaken of 

 some of the movements by which the Lower Tertiaries upon which 

 they rest had acquired their present position and outcrop, and had 

 thus been contemporaneous with some portion at least of that earlier 

 part of the Wealden denudation to which the removal of the Ter- 

 tiaries from the North Downs is due. 



I then caUed especial attention to the circumstance that the posi- 

 tion of the Thames and East Essex gravels in their troughs precluded 

 the possibility of a connexion between them and the Thames river, 

 either in its present or any prior condition, because that part of the 

 Thames valley which lies east of Gravesend, instead of being coinci- 

 dent with the gravel-troughs, cuts at right angles through them — a 

 feature also possessed by the next river to the north, the Crouch, 

 the valley of that river, as well as the portion of the Thames 

 valley just referred to, being entirely destitute of gravel or brick- 

 earth. 



These features, I pointed out, necessitated an admission that the 

 troughs in question had their seaward terminations in the direction 

 of the Weald, because the trough which contained the Thames 

 gravel was absolutely shut in from the north sea by the lofty ridge 

 which separated it from the East-Essex sheet, that ridge not having 

 been opened for the river Thames to reach the North Sea until such 



* Quart. Journ. Greol. Soc. vol. xxi. p. 443. 



t Physical Geology and Geography of Great Britain : 1863 & 64. 



J See papers on the Structure of the Thames Valley and its contained Depo- 

 sits in vol. iii. of Geol. Mag. pp. 57 & 99, and paper on the Structure of the 

 Valleys of the Blackwater and Crouch, and of the East-Essex Gravel, and on the 

 relation of this Gravel to the Denudation of the Weald, ibid. pp. 348 & 398 ; 

 also on the Postglacial Structure of the South-ea^t of England, in Quart. Journ. 

 Geol. Soc. vol. xxiii. p. 394. 



